Laser backrange and marksmanship apparatus and method

ABSTRACT

Methods and systems are provided for making more accurate range and marksmanship determinations in laser-based military engagements. These methods and systems allow a shooter and a target in a laser engagement system to be paired with one another in a substantially unambiguous manner. Such pairing allows the lasers to be used at full power and is particularly well suited for clustered environments in which multiple combatants may be in close proximity to one another. The methods and systems are also particularly well suited for testing new or experimental weapon systems by virtue of the more accurate range and marksmanship estimates provided.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT ON FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

TECHNICAL FIELD OF THE INVENTION

The disclosed embodiments relate generally to war games and militarytraining exercises and, in particular, to systems and methods for moreaccurately determining range and marksmanship during such war games andmilitary training exercises.

BACKGROUND OF THE INVENTION

Modern war games and military training exercises use simulated weaponsfire instead of live fire due to the high cost of munitions andrestrictions on live weapons. The weapons that are simulated may rangefrom small arms carried by soldiers and combat personnel to largecaliber artillery mounted on tanks and armored vehicles. In a typicalengagement simulation system, an infrared laser beam is fired from alaser transmitter mounted on a weapon to simulate firing of the weapontowards a target. A laser receiver at the target detects the laser beamand automatically determines its effect, including any hits, misses,damage, and so forth. The laser typically produces a number of shortduration pulses that encode information about the nature of the weaponbeing simulated.

FIG. 1A illustrates a military training exercise involving an example ofan existing laser engagement system 100 commonly referred to as MILES(multiple integrated laser engagement system). In a typical engagement,a first combatant 102 acquires targeting information on a secondcombatant 104 by aiming a cannon or other weapon at the second combatant104. The first combatant 102 then activates a co-collimated lasertransmitter 106 to simulate direct fire at the second combatant 104. Thelaser transmitter 106 emits a coded burst of laser pulses 108 towardsthe second combatant 104 that encodes within its pattern of pulses thenature and capability of the weapon being simulated by the firstcombatant 102.

At the second combatant 104, a receiver 112 receives and analyzes thelaser pulses 108 from the transmitter 106 to determine, among otherthings, a range or distance from the first combatant 102 in order toestimate the degree of damage or lethality. The receiver 112 may alsoestimate marksmanship from the laser pulse 108, which is a measure ofhow well the second combatant 104 was hit. The range and marksmanshipestimates are then provided to a control system (not expressly shown) ofthe second combatant 104 to use to determine the damage suffered by thesecond combatant 104. These range and marksmanship estimates may also betransmitted to a command center (omitted here) for storage andsubsequent analysis in some cases.

Although not expressly shown, the first combatant 102 may also have areceiver, and the second combatant 104 may also have a transmitter. Infact, the transmitter and the receiver are commonly co-located and mayalso be implemented as a single integrated unit.

As can be seen, it is important that the receiver 112 be able todetermine range and marksmanship for the second combatant 104 asprecisely as possible. Incorrect range estimates may cause a hit to bedeclared on the second combatant 104 even though he/she/it may have beentoo far away based on the capabilities of the particular weapon beingfired. Conversely, a hit may be declared to be inconsequential based onan incorrect estimate when in actuality the opposite is true. Similarly,inaccurate marksmanship estimates may cause a hit to be declared on thewrong combatant where multiple combatants are in close proximity to oneanother. Moreover, even if a hit turned out to be correctly declared,the amount of damage caused by the hit may still be incorrectly assessed(e.g., fatal versus only slightly damaged) if the range and/ormarksmanship estimates are too far off.

For most laser receivers, the range may be estimated from the signalstrength of the received laser pulses. Generally, short range weaponsystem simulators emit low laser power, medium range systems emit mediumpower and long range systems, such as battle tank main guns, emit highlaser power to simulate lethal engagements at longer ranges.Unfortunately, this emitted power technique has a number of drawbacks indirect fire, line-of-sight systems like MILES. For example, dust,debris, smoke, rain, snow, and other atmospheric obstructions may blockor otherwise obscure the path of the laser pulses, resulting in thereception of a weak signal by the receiver, while well within lethalrange, that results in a hit being scored as inconsequential when itshould be scored as lethal. Increasing the laser power to penetrate theobscured atmosphere is not an option because at the laser wavelengthsused, higher power results in a potential for optically damaging theretina of persons who view the beam directly or aided by binoculars orother optical sighting systems. In addition, scattering of the laserbeam by dust and other particles in the atmosphere or from the exitaperture of the laser transmitter can cause combatants that are notbeing aimed at to receive sufficient laser light that they mistakenlydeclare a lethal hit. As a result, one simulated shot may “kill”multiple targets incorrectly. In other words, scattering has the effectof spreading the laser beam out such that the laser beam profile, whichis the area impinged by the laser beam when viewed on a perpendicularplane (as shown in FIG. 1B), appears to diverge and become larger thanit would otherwise be in clear air. The enlarged laser beam profilecaused by scattering effectively expands the “zone of lethality,” whichis a smaller area 110 within the laser beam profile where the lasersignal strength is deemed sufficiently strong to cause damage on atarget. Such an expanded zone of lethality may have an adverse effect onthe accuracy of the marksmanship determination.

The above drawbacks may become exacerbated in clustered environmentswhere other combatants 114, 116, and 118 are in close proximity to thefirst and second combatants 102 and 104, as shown in FIG. 1. In suchclustered environments, ambiguity often arises as to which combatant isshooting and which combatant is being shot. For the above reasons aswell as other drawbacks, operational testing of new or experimentalweapon systems are generally prohibited from being conducted with laserengagement systems such as MILES.

One effort to overcome the line-of-sight limitations associated withdirect fire systems like MILES is to use GPS (global positioning system)to track the geo-positions of the combatants and to exchange messages byradio through a central control when simulating fire or determiningengagement lethality. An example of a GPS-based geo-positioning systemis OneTESS (One Tactical Engagement Simulation System) currently beingdeveloped by AT&T Government Solutions. However, while OneTESS andsimilar GPS-based geo-positioning systems bring the advantages ofindirect fire simulation and may be able to effectively pair combatantsin simple one-to-one and/or long range engagements, these systemspresently lack adequate precision and bandwidth to unambiguously paircombatants where a large number of combatants are in a close range,clustered environment.

Accordingly, what is needed is a laser engagement system, and methodtherefor, that overcomes the deficits and shortcoming of existing andprojected solutions to add unambiguous direct fire pairing to systemssuch as OneTESS and to potentially couple the solution with a laserwavelength choice that is not transmitted and focused on the retina bythe human eye, providing greatly enhanced safety while allowing thelaser transmitter to operate at high enough power to penetrate murkyatmospheres.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to methods and systems forobtaining more accurate range and marksmanship determinations inlaser-based military war games and training engagements. These aspectsallow a shooter and a target in a laser engagement system to be pairedwith one another in a substantially unambiguous manner. Such pairingallows the lasers to be used at full power and is particularly wellsuited for clustered environments in which multiple combatants may be inclose proximity to one another. Aspects of the invention are alsoparticularly well suited for testing new or experimental weapon systemsby virtue of the more accurate range and marksmanship estimatesprovided.

In some aspects, the methods and systems use cooperative measurements ofthe flight time of a laser pulse to more accurately determine thebackwards range, or “backrange,” estimates. As an exemplaryimplementation, these aspects may employ GPS-disciplined oscillators tosynchronize the clock signals of a laser transmitter and a receiver. Thesynchronized clock signals allow a timer at a receiver to be started atalmost exactly the same moment that a laser pulse is fired from atransmitter. This precision lets the receiver very accurately measurethe time it takes for the laser pulse to travel from the transmitter tothe receiver. The flight time may then be converted to a distance orrange estimate via standard mathematical techniques.

Other exemplary implementations of the cooperative backrange aspects ofthe invention may measure both the flight time from a rangefinder to atarget mounted receiver, as well as the flight time from the target backto the rangefinder, in order to obtain a backrange estimate. Suchtwo-way flight time measurement may be made by first transmitting alaser pulse from the rangefinder to the receiver on the target thatstarts a timer at the receiver. The timer is allowed to run while thereflection of the laser pulse is received back at the rangefinder.Another laser pulse from the rangefinder is thereafter transmitted tothe receiver that stops the timer. The measured inter-pulse time, whichincludes the flight time of the initial laser pulse traveling back fromthe receiver and the flight time of the subsequent laser pulse travelingforward to the receiver, may then be converted to a range estimate viastandard conversion techniques. In some implementations, a predefineddelay time may be added between the reception of the reflected laserpulse and the transmission of the subsequent laser pulse to allow forany initialization time that may be needed by the rangefinder. The delaytime may also help minimize the duty cycle of the rangefinder as well asallow for more precise control over the timing of the subsequent laserpulse.

In some aspects, the methods and systems may also use different laserbeam profiles produced by the transmitter to more accurately determinemarksmanship at the receiver. As an exemplary implementation, theseaspects may employ multiple laser beams that each have differentprofiles, or a single laser beam that is capable of transmittingmultiple different profiles. The different beam profiles allow areceiver to be illuminated by some beam components, but not others, suchthat only a receiver in the intended target position is impinged byevery laser profile component or by a required number of laser profiles.Each laser profile may carry a different encoding scheme to allow thetargets to distinguish the different laser profiles from one another.Marksmanship may thereafter be determined according to the number oflaser profiles that impinge a given receiver. In this way, a partiallymissed receiver on the target or other receivers close by on othernon-targeted platforms will not be properly illuminated by a sufficientnumber of beam profile components to declare a high marksmanship hit.

In general, in one aspect, the invention is directed to a system formaking laser-based cooperative time of flight backrange measurements.The system comprises a transmitter operable to emit a laser pulse uponoccurrence of a predefined trigger event for a given engagement. Thesystem further comprises a receiver operable to detect the laser pulsefrom the transmitter, the receiver having a range counter therein andconfigured to start the range counter upon occurrence of a predefinedstart counter event and to stop the range counter upon occurrence of apredefined stop counter event. Whatever count is reached by the rangecounter upon occurrence of the predefined stop counter event may then beused to determine a backrange from the receiver to the transmitter forthe given engagement. It should be noted that the start counter eventmay be the occurrence of a GPS synchronized clock pulse and the stopcounter event may be the detection of a laser pulse. Conversely, thestart counter event may be the detection of a laser pulse and the stopcounter event may be the occurrence of a GPS synchronized clock pulse.Both are solutions that yield the backward range to the transmitterafter mathematical manipulation of the counter value using standardtechniques.

In general, in another aspect, the invention is directed to a method ofmaking laser-based cooperative time of flight backrange measurements.The method comprises the steps of emitting a laser pulse from thetransmitter of a laser rangefinder and detecting the emitted laser pulseat a receiver. The method further comprises the step of starting a rangecounter at the receiver upon occurrence of a predefined start counterevent and stopping the range counter at the receiver upon occurrence ofa predefined stop counter event. The method also comprises the step ofsending a second laser pulse from the rangefinder upon the arrival backat the rangefinder of the first pulse or after a preset delay after thearrival of the first pulse and the subsequent detection of this secondpulse at the receiver. The method finally comprises the step of using acount reached by the range counter upon occurrence of the predefinedstop counter event to determine a backrange from the receiver to thetransmitter for the given engagement.

In general, in yet another aspect, the invention is directed to a systemfor making laser-based marksmanship determinations. The system comprisesa transmitter operable to emit a plurality of laser pulses for a givenengagement, at least two of the laser pulses having laser beam profilesthat span different but overlapping areas. The system further comprisesa receiver operable to detect the plurality of laser pulses from thetransmitter, the receiver configured to distinguish between laser pulseshaving different laser beam profiles. The number of different laser beamprofiles received by the receiver for the given engagement may be thenused to determine a marksmanship of the transmitter by determining howclose to the receiver the transmitted pattern landed.

In general, in still another aspect, the invention is directed to amethod of making laser-based marksmanship determinations. The methodcomprises the step of emitting a plurality of laser pulses from atransmitter for a given engagement, at least two of the laser pulseshaving laser beam profiles that span different but overlapping areas.The method further comprises the step of detecting the plurality oflaser pulses from the transmitter at a receiver, the receiver configuredto distinguish between laser pulses having different laser beamprofiles. The method finally comprises the step of using the number ofthe different laser beam profiles received by the receiver for the givenengagement to determine a marksmanship of the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentfrom the following detailed description and upon reference to thedrawings, wherein:

FIGS. 1A-1B illustrate a laser-based military engagement system and alaser beam profile, respectively, according to the prior art;

FIG. 2 illustrates a laser-based military engagement system that usescooperative time of flight backrange measurements according to aspectsof the invention;

FIG. 3 illustrates another laser-based military engagement system thatuses cooperative time of flight backrange measurements according toaspects of the invention;

FIG. 4 illustrates a rangefinder that may be used for cooperative timeof flight backrange measurements according to aspects of the invention;

FIG. 5 illustrates a receiver that may be used for cooperative time offlight backrange measurements aspects of the invention;

FIG. 6 illustrates a method that may be used for cooperative time offlight backrange measurements aspects of the invention;

FIGS. 7A-7B illustrate exemplary timing diagrams for cooperative time offlight backrange measurements aspects of the invention;

FIG. 8 illustrates a backrange finder having the rangefinder of FIG. 4and the receiver of FIG. 5 integrated as a single unit according toaspects of the invention;

FIG. 9 illustrates a rangefinder that may be used for inter-pulse timecooperative backrange measurements according to aspects of theinvention;

FIG. 10 illustrates a method that may be used for inter-pulse timecooperative backrange measurements according to aspects of the inventionillustrated in FIG. 9;

FIG. 11 illustrates a receiver that may be used for inter-pulse timecooperative backrange measurements according to aspects of theinvention;

FIG. 12 illustrates a method that may be used for inter-pulse timecooperative backrange measurements according to aspects of the inventionillustrated in FIG. 12;

FIGS. 13A-13B illustrate exemplary timing diagrams for inter-pulse timecooperative backrange measurements according to aspects of theinvention;

FIG. 14 illustrates a backrange finder having the rangefinder of FIG. 9and the receiver of FIG. 11 integrated as a single unit according toaspects of the invention;

FIG. 15 illustrates a rangefinder that may be used for marksmanshipdeterminations based on multiple laser beam profiles according toaspects of the invention;

FIG. 16 illustrates a receiver that may be used for marksmanshipdeterminations based on multiple laser beam profiles according toaspects of the invention;

FIG. 17 illustrates a method that may be used for marksmanshipdeterminations based on multiple laser beam profiles according toaspects of the invention;

FIGS. 18A-18B illustrate a timing diagram and laser beam profiles,respectively, for marksmanship determinations based on multiple laserbeam profiles according to aspects of the invention;

FIGS. 19A-19B illustrate another timing diagram and laser beam profiles,respectively, for marksmanship determinations based on multiple laserbeam profiles according to aspects of the invention; and

FIG. 20 illustrates a backrange finder having the rangefinder of FIG. 15and the receiver of FIG. 16 integrated as a single unit according toaspects of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The drawings described above and the written description of specificstructures and functions below are not presented to limit the scope ofwhat has been invented or the scope of the appended claims. Rather, thedrawings and written description are provided to teach any personskilled in the art to make and use the inventions for which patentprotection is sought. Those skilled in the art will appreciate that notall features of a commercial embodiment of the inventions are describedor shown for the sake of clarity and understanding.

Persons of skill in this art will also appreciate that the developmentof an actual commercial embodiment incorporating aspects of theinventions will require numerous implementation-specific decisions toachieve the developer's ultimate goal for the commercial embodiment.Such implementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would be, nevertheless, a routine undertaking for those of skillin this art having benefit of this disclosure.

It should be understood that the embodiments disclosed and taught hereinare susceptible to numerous and various modifications and alternativeforms. Thus, the use of a singular term, such as, but not limited to,“a” and the like, is not intended as limiting of the number of items.Also, the use of relational terms, such as, but not limited to, “top,”“bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” andthe like, are used in the written description for clarity in specificreference to the drawings and are not intended to limit the scope of theinvention or the appended claims.

Particular embodiments are now described with reference to blockdiagrams and/or operational illustrations of methods. It should beunderstood that each block of the block diagrams and/or operationalillustrations, and combinations of blocks in the block diagrams and/oroperational illustrations, may be implemented by analog and/or digitalhardware, and/or computer program instructions. Computing instructionsfor use with or by the embodiments disclosed herein may be written in anobject oriented programming language, conventional proceduralprogramming language, or lower-level code, such as assembly languageand/or microcode. The instructions may be executed entirely on a singleprocessor and/or across multiple processors, as a stand-alone softwarepackage or as part of another software package. Such computinginstructions may be provided to a stand-alone processor, ageneral-purpose computer, special-purpose computer, ASIC,field-programmable gate array (FPGA), and/or other programmable dataprocessing system.

The executed instructions may create structures and functions forimplementing the actions specified in the mentioned block diagramsand/or operational illustrations. The functions/actions/structures notedin the drawings may also occur out of the order noted in the blockdiagrams and/or operational illustrations. For example, two operationsshown as occurring in succession, in fact, may be executed substantiallyconcurrently or the operations may be executed in the reverse order,depending on the functionality/acts/structure involved.

As mentioned above, certain aspects of the invention employ cooperativetime of flight measurements to more accurately determine backrange inlaser-based military engagement systems. Other aspects of the inventionrely on the use of multiple different laser beam profiles to moreaccurately determine marksmanship. The following description focusesfirst on the cooperative time of flight backrange aspects of theinvention, as illustrated in FIGS. 1-13. Other aspects of the inventionthat pertain to the use of multiple laser beam profiles are thendiscussed with respect to FIGS. 14-19.

In general, cooperative time of flight backrange measurements allow ashooter and a target to be paired with one another in an unambiguousmanner, even in crowded and clustered environments. The term“cooperative” is used herein to mean that the laser receiver isoperating in concert or coordination with the laser transmitter, orrangefinder, as opposed to simply detecting a laser pulse from therangefinder. The extent and type of concerted or coordinated action thatexists between the rangefinder and the receiver may vary according toeach implementation, such that there may be more concerted action insome cases and less in others. However, the presence of any amount ofconcerted or coordinated action is in stark contrast to existingsolutions where the rangefinder and the receiver operate entirelyindependent of one another.

The cooperative time of flight backrange measurement aspects of theinvention may be implemented in at least two ways.

As an example, cooperative time of flight backrange measurements may bemade by measuring the flight time in not just one, but both directionsbetween a rangefinder and a receiver. Such a bi-directional flight timemeasurement may be made by transmitting a laser pulse from therangefinder to the receiver to start a timer at the receiver, then usingthe reflection from that laser pulse to trigger another laser pulse tothe receiver that stops the timer. The combined flight times of thereflected laser pulse and the subsequent laser pulse, called the“inter-pulse time,” may then be used to determine the distance betweenthe rangefinder and the receiver. In some implementations, a predefineddelay time may be added between the return of the initial laser pulseand the firing of the follow-up laser pulse to account for anyinitialization time that may be needed at the rangefinder. This delaytime may also help reduce the duty cycle of the rangefinder whileenabling more precise scheduling of the follow-up laser pulse.

In other implementations, highly accurate GPS satellite clock signalsmay be used to synchronize the clocks at the rangefinder and thereceiver in order to make the cooperative backrange measurements. GPSsatellites are known by those having ordinary skill in the art togenerate very accurate time information in addition to geo-positioninginformation. The time information provided by the GPS satellites isreferenced to a universal time constant (UTC) and may generally beacquired through GPS receivers. Various devices and applications maythen synchronize their clocks to the GPS satellite clocks via the GPSreceivers to ensure highly accurate timekeeping.

A GPS-based implementation may be seen in FIG. 2 where a laserengagement system 200 is shown that uses GPS satellite time to makecooperative time of flight backrange measurements. As can be seen, theGPS-synchronized laser engagement system 200 comprises a GPS-based lasertransmitter 202 mounted on a shooter 204 (Combatant A) and a GPS-basedreceiver 206 mounted on a target 208 (Combatant B). The GPS-basedtransmitter 202 and the GPS-based receiver 206 are configured to receivetime information from a GPS satellite 210 via satellite transmissions212. This GPS satellite time information may then be used to measure theflight time for a laser pulse arriving at the GPS-based receiver 206from the GPS-based transmitter 202. In some implementations, the shooter204 and the target 208 may additionally communicate measurements andother information to a command center 214 via wireless transmissions 216for storage and analysis.

For economy of the description and also for clarity of the figure, onlyone shooter 204 having a GPS-based laser transmitter 202, one target 208having a GPS-based receiver 206, and one GPS satellite 210 are shown inFIG. 2. It should be understood, however, that the GPS-synchronizedlaser engagement system 200 may comprise multiple GPS-based transmitters202 and multiple GPS-based receivers 206, each of which may receive GPStime information from the same or different GPS satellites 210.Moreover, each shooter 204 and each target 208 may have both a GPS-basedtransmitter 202 and a GPS-based receiver 206, either as discrete unitsthat may or may not be co-located, or as a single integrated unit,depending on the particular application. Finally, although the shooter204 and the target 208 are depicted as military vehicles in FIG. 2,those having ordinary skill in the art will understand that one or moreof these combatants may instead be an individual combat personnel. Inthe latter case, the GPS-based transmitter 202 and the GPS-basedreceiver 206 may be worn or otherwise carried by the combat personnel asappropriate.

FIG. 3 illustrates an alternative example of a GPS-synchronized laserengagement system 300 into which a GPS base station is used instead ofGPS satellites. This GPS-synchronized laser engagement system 300 issimilar to the GPS-synchronized laser engagement system 200 of FIG. 2insofar as it comprises a GPS-based laser transmitter 302 mounted on ashooter 304, a GPS-based receiver 306 mounted on a target 308, and acommand center 314 to which shooter and target information may betransferred via wireless transmissions 316. These components 302-314 aresimilar to their counterparts in FIG. 2 and are therefore not separatelydescribed herein. As can be seen, instead of a GPS satellite, a GPS basestation 310 may be provided to transmit GPS time information to theGPS-based rangefinder 302 and the GPS-based receiver 306. Such a GPSbase station 310 may function essentially as a transponder for the GPSsatellite(s) and, owing to its closer proximity, may help minimize anydrift that may develop between the GPS-based transmitter 302 and theGPS-based receiver 306.

Turning now to FIG. 4, a more detailed example is shown of a GPS-basedrangefinder 400 according to aspects of the invention. In most respects,the GPS-based rangefinder 400 is similar to standard laser rangefindersthat are commercially available from a number of manufacturers,including Bushnell Corporation of Overland Park, Kans., GoodrichCorporation of Charlotte, N.C., and Vectronix, Inc. of Leesburg, Va.Such laser rangefinders operate generally by firing a short laser pulseor pulses towards a target and measuring the time it takes for the laserpulse or pulses to reflect off the target and return to therangefinders.

The GPS-based rangefinder 400 has an additional feature, however, inthat the firing of the laser pulse is synchronized to a GPS receiverclock. GPS satellites are configured to generate clock pulses, one pulseper second (1 PPS), in GPS receivers, at almost exactly the same time(e.g., within 25 nanoseconds according to some sources) provided thatthe GPS receivers are substantially within the coverage of the same GPSsatellite constellation. This means that GPS receivers “tick”substantially in unison regardless of where they are on or above thesurface of the Earth. This “tick” may then be used to synchronize thetiming of various events, such as the firing of a laser pulse or thestarting of a timer. The fact that the “tick” for one event and the“tick” for another event may need to be derived from different GPSreceivers has little or no effect on the synchronization due to thecapability of the GPS satellite system in providing accurate time stampsto GPS receivers illuminated by substantially the same constellation ofGPS satellites.

Synchronizing an event with a “tick” from a GPS receiver may beaccomplished by referencing or disciplining an oscillator, such as aquartz crystal oscillator or other highly stable oscillator, to theclock “ticks” produced within the GPS receiver by the GPS satellitesystem. Techniques for creating GPS-disciplined oscillators are wellknown to those having ordinary skill in the art as evidenced by, forexample, U.S. Pat. No. 5,440,313 (“GPS Synchronized Frequency/TimeSource”) and U.S. Pat. No. 5,717,404 (“GPS Reference Clock Generator”),which are incorporated herein by reference. In general, a GPS receivermay be used to obtain GPS timing information, including the 1 PPS“tick,” from the GPS satellites and provide the information to acontroller. The controller then compares the GPS timing information tothe output of a voltage-controlled oscillator (VCO). Any differencebetween the frequency of the VCO output (which may need to be divided byan appropriate factor) and the GPS receiver is provided as a feedbacksignal to the VCO by the controller in order to adjust the VCO output.

In accordance with aspects of the invention, the GPS-based rangefinder400 may be equipped with a GPS-disciplined oscillator that may be usedto regulate the timing of laser pulses from the GPS-based rangefinder400. This is shown in a FIG. 4, where the GPS-based rangefinder 400 canbe seen to comprise a GPS-based timing system 402, a laser detector 404,a laser transmitter 406, and a rangefinder control system 408, amongother functional components. One or more data buses 410 may be providedto connect the various functional components 402-408 together as needed.In general, the laser detector 404 functions to detect laser pulsesreceived by the GPS-based rangefinder 400 (e.g., reflected laserpulses), the laser transmitter 406 functions to emit laser pulses, andthe rangefinder control system 408 functions to control the operation ofthe laser detector 404 and the laser transmitter 406.

Firing of the laser pulses from the laser detector 404 may be regulatedby the GPS-based timing system 402 via a trigger signal, which isessentially a clock signal, from the GPS-based timing system 402. Tothis end, the GPS-based timing system 402 may comprise a GPS receiver412 and a GPS-disciplined clock 414, among other components. The GPSreceiver 412 produces GPS clock “ticks” from the GPS satellite signalsand provides the GPS clock “ticks” to the GPS-disciplined clock 414. TheGPS-disciplined clock 414 may then use the GPS clock “ticks” to generatea clock signal. In one implementation, the GPS-disciplined clock 114 maygenerate the clock signal by using the GPS clock “ticks” to disciplinean oscillator 416 in a manner known to those having ordinary skill inthe art. The output of this GPS-disciplined oscillator 416, which may bea 1 MHz, 5 MHz, 10 MHz, 20 MHz, and so forth signal, may then beconverted by the GPS-disciplined clock 414 into a clock signal having adesired frequency, such as 1 Hz, 5 Hz, 10 Hz, 20 Hz, and so forth. Thewaveforms that constitute the clock signal of the GPS-disciplined clock414 may thereafter be provided to the laser transmitter 406 to controlfiring of the laser detector 404.

In general operation, when a shooter executes a firing sequence for theGPS-based rangefinder 400, a control signal is sent from the rangefindercontrol system 408 to the laser transmitter 406 to fire the lasertransmitter 406. However, no laser pulse is actually fired by the lasertransmitter 406 until the instant a clock signal is received from theGPS-disciplined clock 414. This clock signal may be in the form of arising edge, a falling edge, a logic level, and the like, depending onthe particular configuration of the laser transmitter 406. When theclock signal from the GPS-disciplined clock 414 is received, the lasertransmitter 406 immediately fires a laser pulse, then waits for the nextclock signal. Of course, if no control signal is received from therangefinder control system 408, then no laser pulse is fired regardlessof whether clock signals from the GPS-disciplined clock 414 continue tobe received.

In a typical arrangement, the clock signal from the GPS-disciplinedclock 414 may have a frequency of 10 Hz, resulting in 10 laser pulsesbeing fired per second. In other arrangements, however, the lasertransmitter 406 may be internally configured to fire not one, but astring of laser pulses at a time. For example, consider a case where theGPS-disciplined clock 414 generates a 1 Hz clock signal, but the lasertransmitter 406 is a type that, once activated, will automatically firea burst of laser pulses, say, 5 laser pulses, in rapid succession. Inthat case, it is contemplated that only the initial laser pulse, namely,the one that coincides with the receipt of a waveform (e.g., risingedge, falling edge, logic level, etc.) from the GPS-disciplined clocksignal, need be used for the cooperative backrange measurement. Theremaining laser pulses in the string of laser pulses may also be used ifdesired, or they may simply be ignored, depending on the particularapplication.

On the target side, the laser pulse from the laser transmitter 406 isreceived by a GPS-based receiver 500, an example of which is illustratedin FIG. 5. Like the GPS-based rangefinder 400, the GPS-based receiver500 is otherwise similar to commercially available laser receiversexcept it is equipped with a range counter that is synchronized to a GPSsatellite clock. As can be seen, the GPS-based receiver 500 comprises aGPS-based timing system 502, a laser detector 504, a range counter 506,and a receiver control system 508, among other functional components.One or more data buses 510 may be provided to connect the variousfunctional components 502-508 together as needed. In general, the laserdetector 504 functions to detect laser pulses received by the GPS-basedreceiver 500, the range counter 506 functions as a high frequency (e.g.,10 MHz, and 20 MHz, 30 MHz, 40 MHz, etc.) timer to measure the flighttime for one or more of the received laser pulses, and the receivercontrol system 508 functions to control operation of the laser detector504 and the range counter 506.

In accordance with aspects of the invention, the range counter 506 maybe initiated by a start signal in the form of a clock signal from theGPS-based timing system 502. To this end, the GPS-based timing system502 may comprise a GPS receiver 512 and a GPS-disciplined clock 514,among other components. These GPS-based components are similar to theircounterparts in the GPS-based timing system 402 of FIG. 4 and aretherefore not discussed in detail here. Suffice it to say, theGPS-disciplined clock 514 may generate a clock signal using aGPS-disciplined oscillator 516 that is synchronized to a GPS satelliteclock. The clock signal here may have the same frequency (e.g., 1 Hz, 5Hz, 10 Hz, 20 Hz, etc.) as the clock signal from the GPS-disciplinedclock 416 of FIG. 4. Moreover, the two clock signals may be almostperfectly in phase with one another (e.g., within 25 nanoseconds) byvirtue of their GPS disciplined oscillators 416 and 516 being referencedto GPS satellite clocks.

The clock signal from the GPS-disciplined clock 514 may then be used toregulate the starting of the range counter 506 so that it coincides(e.g., within 25 nanoseconds) with the firing of the laser pulse fromthe laser transmitter 406. This means of course that the clock signalfrom the GPS-disciplined clock 514 should have the same frequency (e.g.,10 Hz) as the clock signal from the GPS-disciplined clock 414 of FIG. 4.To the extent any drift may develop between the two clock signals, suchdrift should be compensated each time the GPS-disciplined oscillators416 and 516 are synchronized back to their respective GPS satelliteclocks. This temporal alignment of the clock signals from the twoGPS-disciplined clocks 414 and 514, combined with the high frequency ofthe range counter 506, produces a very precise measurement of the flighttime for a given laser pulse arriving at the GPS-based receiver 500. Theflight time may then be converted to an estimate of the backrange ordistance from the target to the shooter in a manner known to thosehaving ordinary skill in the art.

Flight time measurement may begin generally when the range counter 506receives a waveform (e.g., rising edge, falling edge, logic level, etc.)from the clock signal of the GPS-disciplined clock 514. At that instant,the range counter 506 starts counting, for example, at a rate of 30 MHz,then stops counting when a laser pulse is received by the laser detector504. When another clock signal waveform is received from theGPS-disciplined clock 514, the range counter 506 starts counting againuntil another laser pulse is received, and so on. Of course, if no laserpulse is received by the laser detector 504 by the time the next clocksignal from the GPS-disciplined clock 514 is received, then the rangecounter 506 simply overflows into a restart.

Assuming there is not an overflow, whatever count the range counter 506stops on when a laser pulse is received by the laser detector 504 may beread or otherwise captured by the receiver control system 508 and usedas a measure of the flight time for the laser pulse. This count may thenbe converted to a backrange measurement by applying calculations wellknown to those having ordinary skill in the art, for example:backrange=count*speed of light/range counter frequency (the speed oflight is denoted herein by the letter “c”). It may also be desirable insome cases to take a range counter reading for several laser pulses(e.g., 3, 5, 7, etc.) and use either the average count, median count,maximum count, minimum count, or some other mathematical and/orstatistical variation to calculate the backrange measurement.

The foregoing backrange measurement process may be implemented in thereceiver control system 508 in the form of a backrange module 516 forsome aspects of the invention. This backrange module 516 may be asoftware module downloaded to and executed on the receiver controlsystem 508, a hardware module fitted to or integrated with the receivercontrol system 508, or a combination of both software and hardware. Thebackrange module 516 may also be one of several smaller componentsmaking up a larger overall software program and/or hardware component onthe receiver control system 508. In any event, such a backrange module516 may then be operated to measure the backrange from the target to theshooter in the manner described above.

General guidelines for operation of the backrange module 516 areillustrated in the form of a flowchart 600 in FIG. 6. As can be seen,the flowchart 600 begins at block 602 where the range counter 506 isstarted/restarted with a clock signal waveform from the GPS-disciplinedclock 514. At block 604, the laser detector 504 is monitored forincoming laser pulses, and a determination is made at block 606 as towhether a laser pulse has been detected. If a laser pulse is detected,then at block 608, the range counter 506 is stopped and the count isread or otherwise captured. The count is thereafter used to calculatethe backrange in a manner known to those having ordinary skill in theart at block 610. If no laser pulse is detected at block 606, then adetermination is made at block 612 has to whether the range counter 506has overflowed and restarted (i.e., meaning another GPS-disciplinedclock signal waveform has been received). If there is no overflow, thenthe flowchart 600 returns to block 604 where the laser detector 602 isonce again monitored. On the other hand, if there is an overflow, thenthe flowchart 600 returns to block 602 where the process is restarted.

FIGS. 7A-7B illustrate exemplary timing diagrams for the above backrangemeasurements according to aspects of the invention. Referring first toFIG. 7A, the horizontal lines indicated at 700 and 702 are time linesfor a GPS-based rangefinder and a GPS-based receiver, respectively. Thelong vertical lines, one of which is indicated at 704, represent thewaveforms of a 10 Hz clock signals from GPS-disciplined clocks. Theseclock signal waveforms 704 from the GPS-disciplined clocks occur atalmost exactly the same time in both timelines 700 and 702 for thereasons explained above and are therefore represented by one verticalline that spans both timelines. Laser pulses, one of which is indicatedat 706, are represented by the short vertical lines. As can be seen, theclock signal waveform 704 that triggers the firing of a laser pulse 706from the rangefinder nearly simultaneously starts a range counter at thereceiver. The range counter stops counting when the laser pulse isreceived at the receiver. The flight time is simply the time it took forthe laser pulse to travel from the rangefinder to the receiver. Thebackrange may then be determined by multiplying the flight time by thespeed of light.

FIG. 7B illustrates an alternative implementation where the trailingtime for a laser pulse is measured instead of its flight time. As can beseen in this implementation, the range counter in the GPS-based receiverstarts counting when a laser pulse is received and stops counting uponoccurrence of a clock signal from the GPS-disciplined clock. Thetrailing time is simply the time between the reception of the laserpulse and the occurrence of the clock signal waveform. The flight timemay then be found by subtracting the trailing time from the clock signalwaveform interval, which would be 100 microseconds for a 10 Hz clocksignal, for example. An advantage of this arrangement is that the rangecounter begins counting only upon reception of a laser pulse instead ofupon occurrence of a clock signal waveform, which may significantlyreduce the duty cycle of the range counter if there are long periodsbetween laser pulse firings.

Note in the foregoing description that if the GPS-based rangefinder 400or the GPS-based receiver 500 is modeled after commercially availabledevices, they may already have an internal clock system that regulatesdevice operation. In that case, the GPS-based timing systems 402 and 502may be retrofitted as either a replacement for, or a supplement to, anyexisting internal clock systems. If deployed as a replacement, thefrequencies of the clock signals from the GPS-disciplined oscillators416 and 516 may be divided or multiplied as needed to match thefrequencies of the internal clock systems. If deployed as a supplement,the GPS-disciplined clock 414 may be used to regulate the firing of thelaser pulses, with other device functions continuing to be regulated bythe internal clock systems.

In addition, instead of separate or possibly co-located units as shownin FIGS. 4 and 5, the GPS-based rangefinder 400 and the GPS-basedreceiver 500 may be combined into a single integrated GPS-basedbackrange finder 800, illustrated in FIG. 8. As can be seen, thisintegrated GPS-based backrange finder 800 comprises a number offunctional components, including a GPS-based timing system 802, a laserdetector 804, a range counter 806, a control system 808 having abackrange module 810 therein for determining backrange measurements, anda laser transmitter 812. One or more data buses 814 may be provided toconnect the various components 802-812 together as needed. In accordancewith aspects of the invention, the GPS-based timing system 802 maycomprise a GPS receiver 816 and a GPS-disciplined clock 818 having aGPS-disciplined oscillator 820 therein for generating clock signals thatare synchronized to a GPS satellite clock. These components 802-820 ofthe integrated GPS-based backrange finder 800 operate in a similarmanner to their counterparts in FIGS. 4 and 5 and therefore a detaileddescription is omitted here.

While use of GPS satellite clock signals to make cooperative backrangemeasurements clearly provides advantages over existing solutions, asmentioned at the outset, aspects of the invention also contemplateanother way of making cooperative backrange measurements. For example,cooperative time of flight backrange measurements may be made bymeasuring the time of flight in both directions between a rangefinderand a receiver. This back-and-forth measurement may be made bytransmitting a laser pulse from the rangefinder to the receiver to starta timer at the receiver, then using the reflection from that laser pulseto trigger a second laser pulse from the rangefinder that stops thetimer. The return flight time of the start laser pulse and the forwardflight time of the stop laser pulse, which together make up theinter-pulse time, may then be used to determine the distance between therangefinder and the receiver. In some implementations, a delay of apredefined length of time may be inserted between the start laser pulseand the stop laser pulse to account for any pre-firing processing thatmay be needed at the rangefinder. The predefined delay may help fulfillminimize the duty cycle of the rangefinder, as well as to more preciselycontrol the timing of the second laser pulse.

FIG. 9 illustrates an example of a rangefinder 900 according to aspectsof the invention that may be used to make cooperative backrangeestimates using the inter-pulse time technique described above. Therangefinder 900 generally resembles commercially available rangefindersexcept that it may be configured to use the reflection from one laserpulse to trigger the transmission of another laser pulse. As can beseen, the rangefinder 900 comprises a number of functional components,including a timing system 902, a laser detector 904, a laser transmitter906, and a rangefinder control system 908. One or more data buses 910may be provided to connect the various functional components 902-908together as needed. In general, the laser detector 904 functions todetect laser pulses received by the rangefinder 900 (e.g., reflectedlaser pulses), the laser transmitter 906 functions to emit laser pulses,and the rangefinder control system 908 functions to control theoperation of the laser detector 904 and the laser transmitter 906. Thetiming system 902 generates one or more clock signals that may be usedto regulate the internal operation of the rangefinder 900 and, for thatpurpose, may include an oscillator 912 and a clock signal generator 914connected thereto.

As mentioned above, the rangefinder 900 may be configured to fire alaser pulse, wait for the reflection from that laser pulse to return,then fire another laser pulse either immediately or after a predefineddelay time. This cooperative firing sequence is in contradistinction tocommercially available rangefinders that simply fire laser pulseswithout regard to when or even whether the fired laser pulses arereturned. In some implementations, the cooperative firing sequence maybe embodied in the rangefinder control system 908 in the form of acooperative firing module 916 for some aspects of the invention. As withother modules herein, the cooperative firing module 916 may be asoftware module downloaded to and executed on the rangefinder controlsystem 908, a hardware module fitted to or integrated with therangefinder control system 908, or a combination of both software andhardware.

General guidelines for operation of the cooperative firing module 916are illustrated in the form of a flowchart 1000 in FIG. 10. As can beseen, the flowchart 1000 begins at block 1002 where a laser pulse isfired from the laser transmitter 906. This laser pulse may be fired inaccordance standard triggering operation known to those having ordinaryskill in the art (e.g., by sending a trigger signal from the rangefindercontrol system 908 to the laser transmitter 906, etc.). At block 1004,the laser detector 904 is monitored for the return of the laser pulse(e.g., after it has reflected off an intended target). At block 1006, adetermination is made as to whether the return laser pulse has beendetected by the laser detector 904. Detection of the return laser pulsemay be accomplished using techniques commonly known to those havingordinary skill in the art, for example, by determining the modulation orencoding of the laser pulse.

If the answer at block 1006 is yes, then at block 1008, a predefineddelay time (e.g., 10 μs, 20 μs, etc.) is carried out in order to givethe laser transmitter 906 sufficient time to execute any initializationor pre-firing processing. This delay also helps minimize the duty cycleof the laser transmitter 906, as well as allowing more precise controlof when the second laser pulse is fired. The second laser pulse is thenfired from the laser transmitter 906 at block 1010.

On the other hand, if the answer at block 1006 is no, then adetermination is made at block 1012 as to whether the return laser pulsemay have expired based on one or more predetermined criteria (e.g.,elapsed time). If the return laser pulse has not expired, then theflowchart 1000 continues with monitoring of the laser detector 904 atblock 1004. If the return laser pulse has expired, then no additionallaser pulses are fired, and the flowchart 1000 terminates.

At the target end, the initial laser pulse from the laser transmitter906 is received by a receiver 1100, an example of which is illustratedin FIG. 11. The receiver 1100 is similar to commercially available laserreceivers except it is equipped with a range counter that provides ameasure of the inter-pulse time described above. As can be seen, thereceiver 1100 comprises a timing system 1102, a laser detector 1104, arange counter 1106, and a receiver control system 1108, among otherfunctional components. One or more data buses 1110 may be provided toconnect the various functional components 1102-1108 together as needed.The laser detector 1104 functions to detect laser pulses received by thereceiver 1100, the range counter 1106 functions as a high frequency(e.g., 10 MHz, and 20 MHz, 30 MHz, 90 MHz, etc.) timer to measure theflight time back and forth between the rangefinder 900 and the receiver1100, and the receiver control system 1108 functions to controloperation of the laser detector 1104 and the range counter 1106. Anoscillator 1112 and a clock signal generator 1114 may be provided in thetiming system 1102 to allow the timing system 1102 to regulate theinternal operation of the receiver 1100.

In accordance with aspects of the invention, the range counter 1106 maystart counting upon receipt of a first laser pulse, or start laserpulse, at the laser detector 1104 from the laser transmitter 906.Preferably, the range counter 1106 is a high frequency counter, forexample, 20 MHz, 30 MHz, 40 MHz, and the like, in order to providegreater accuracy. The range counter 1106 is allowed to continue countinguntil receipt of a second laser pulse, or stop laser pulse, from thelaser transmitter 906. Note that the stop pulse should be a laser pulsefrom the same rangefinder 900 and not some other rangefinder. Detectionof the stop laser pulse may be accomplished using techniques commonlyknown to those having ordinary skill in the art, for example, bydiscerning the modulation or encoding of the laser pulse.

If no stop pulse from the laser transmitter 906 of the same rangefinder900 is received within a predefined amount of time, for example, 10 μs,20 μs, 30 μs, and so forth, then the range counter 1106 simply overflowsand is reset. The range counter 1106 thereafter starts counting againupon receipt of the next laser pulse from the laser transmitter 906.

Whatever count the range counter 1106 stops on when the stop pulse isreceived may be read or otherwise captured by the receiver controlsystem 1108 and used as a measure of the inter-pulse time. This countmay then be converted to a backrange measurement by applying theappropriate calculations. It may also be desirable in some cases to takeseveral range counter readings (e.g., 4, 9, 13, etc.) and use either theaverage count, median count, maximum count, minimum count, or some othermathematical and/or statistical variation to calculate the backrangemeasurement.

The foregoing counting process may be implemented in the receivercontrol system 1108 in the form of a backrange module 1116 for someaspects of the invention. As with previous modules, this backrangemodule 1116 may be a software module downloaded to and executed on thereceiver control system 1108, a hardware module fitted to or integratedwith the receiver control system 1108, or a combination of both softwareand hardware. The backrange module 1116 may also be one of severalsmaller components making up a larger overall software program and/orhardware component on the receiver control system 1108. Such a backrangemodule 1116 may then be operated to measure the backrange from therangefinder 900 to the receiver 1100 in the manner described previously.

General guidelines for operation of the backrange module 1116 areillustrated in the form of a flowchart 1200 in FIG. 12. As can be seen,the flowchart 1200 begins at block 1202 where the laser detector 1104 ismonitored for receipt of a laser pulse. At block 1204, a determinationis made as to whether a laser pulse has been detected. The range counter1106 may be started at block 1206 if the answer to block 1204 is yes, orthe laser detector 1104 may continue to be monitored at block 1202 ifthe answer to block 1204 is no. At block 1208, the laser detector

At block 1208, the laser detector 1104 is monitored again for receptionof another laser pulse from the laser transmitter 906 of the samerangefinder 900. A determination is made at block 1210 as to whether thenext laser pulse has been detected. The range counter 1106 may bestopped and the count thereof read at block 1212 if the answer to block1210 is yes. The count is thereafter used to calculate the backrange ina manner known to those having ordinary skill in the art at block 1214.

If no laser pulse is detected at block 1208, then a determination ismade at block 1216 has to whether the range counter 1106 has overflowed.If there is no overflow, then the flowchart 1200 returns to block 1208where monitoring of the laser detector 1104 continues. On the otherhand, if there is an overflow, then the range counter 1106 is reset theflowchart 1200 returns to block 1202 where the process may be restarted.

FIGS. 13A-13B illustrate exemplary timing diagrams for backrangemeasurements according to the inter-pulse time aspects of the invention.Referring first to FIG. 13A, the horizontal lines 1300 and 1302 are timelines for a rangefinder and a receiver, respectively. As can be seen,the cooperative backrange measurement process begins when a laser pulse1304 is fired from a rangefinder and thereafter received by a receiver.The time it takes for the laser pulse 1304 to travel from therangefinder to the receiver is indicated on the timing diagram as“Flight Time 1.” At the receiver, the received laser pulse 1306activates a timer and at the same time is reflected back towards therangefinder. The time it takes for the reflected laser pulse 1308 totravel from the receiver back to the rangefinder is indicated on thetiming diagram as “Return Time.” Detection of the reflected laser pulse1308 at the rangefinder triggers the firing of another laser pulse 1310from the rangefinder to the receiver. The time it takes for this otherlaser pulse 1310 to travel from the rangefinder to the receiver isindicated on the timing diagram as “Flight Time 2.” The duration of“Flight Time 1” is equal to the duration of “Flight Time 2” in mostcases. At the receiver, the detection of the received laser pulse 1312stops the timer. The total time measured by the timer at the receiver istherefore “Return Time” plus “Flight Time 2” and is referred to as the“Inter-Pulse Time” (t_(p)) on the timing diagram. The backrange may thenbe calculated by multiplying the “Inter-Pulse Time” by the speed oflight and dividing by two.

In the diagram of FIG. 13A, it is assumed that the rangefinder and thereceiver are sufficiently far apart that the rangefinder has enough timeafter firing the first laser pulse 1304 to complete any pre-firingprocessing such that there is no delay before firing the second laserpulse 1310 immediately upon reception of the reflected laser pulse 1308.However, in the event an initialization period is needed by therangefinder, a preset delay time may be inserted between the receptionof the reflected laser pulse 1308 and the firing of the second laserpulse 1310, as shown in FIG. 13B. Such a preset delay time, which wouldbe known beforehand by the receiver, may help minimize the duty cycle onthe rangefinder, as well as allowing more precise control of when thesecond laser pulse is fired. The delay time is indicated on the timingdiagram of FIG. 13B as “Delay Time” (t_(d)) and may be on the order of10 μs, 20 μs, 30 μs, and so forth. The “Inter-Pulse Time” (t_(p))measured by the timer therefore becomes “Return Time” plus “Flight Time2” plus “Delay Time,” and the backrange is then the “Inter-Pulse Time”minus the “Delay Time” multiplied by the speed of light and divided bytwo.

In some implementations, instead of separate or possibly co-locatedrangefinder 900 and receiver 1100 as shown in FIGS. 9 and 11, therangefinder 900 and the receiver 1100 may be combined into a singleintegrated backrange finder 1400, illustrated in FIG. 14. As can beseen, this integrated backrange finder 1400 comprises a timing system1402, a laser detector 1404, a range counter 1406, a control system1408, and a laser transmitter 1410. One or more data buses 1412 may beprovided to connect the various components 1402-1410 together as needed.The timing system 1402 provides the clock signals that regulate theoperation of the integrated backrange finder 1400 and, to that end, mayinclude an oscillator 1414 and a clock signal generator 1416. Inaccordance with aspects of the invention, the control system 1408 maycomprise a cooperative firing module 1418 for controlling the timing ofthe laser pulses fired from the laser transmitter 1410 and a backrangemodule 1420 for determining backrange measurements. These components1402-1420 of the integrated backrange finder 1400 operate in a similarmanner to their counterparts in FIGS. 9 and 11 and therefore a detaileddescription is not necessary here.

In addition to cooperative backrange measurements, aspects of theinvention also allows for more accurate marksmanship determinations, orhow well a target was hit, to be obtained. These marksmanship aspects ofthe invention may be implemented, for example, by transmitting laserpulses that have different profiles in order to more clearly identify anintended target. The different laser profiles may be achieved by usingmultiple laser beams that each have a different profile, or by using asingle laser beam that is capable of several different profiles, or acombination of both. The different beam profiles allow some receivers tobe impinged, but not others, such that only the intended target isilluminated by every laser profile or by a required number of laserprofiles. Each laser profile may have a different encoding scheme toallow the targets to distinguish the different laser profiles from oneanother. Marksmanship may thereafter be determined according to thenumber of laser profiles that illuminate a given target.

FIG. 15 illustrates an example of a rangefinder 1500 according toaspects of the invention that uses multiple laser beam profiles todetermine marksmanship. As with previous rangefinders herein, therangefinder 1500 may be similar to commercially available rangefindersexcept that it may be configured with multiple laser beam profiles. Ascan be seen, the rangefinder 1500 comprises a number of functionalcomponents, including a timing system 1502, a laser detector 1504, a fanbeam transmitter 1506, and a rangefinder control system 1508. One ormore data buses 1510 may be provided to connect the various functionalcomponents 1502-1508 together as needed. An oscillator 1512 and a clocksignal generator 1514 may be provided in the timing system 1502 to allowthe timing system 1502 to regulate the internal operation of therangefinder 1500.

In accordance with aspects of invention, the fan beam transmitter 1506may be configured to emit laser pulses having multiple different beamprofiles. Such a fan beam transmitter 1506 may comprise a single fanlaser or it may comprise several fan lasers arrayed together. A fanlaser, as understood by those having ordinary skill in the art, is alaser that is capable of outputting a fan-shaped beam. Such fan lasersare generally well known in the laser art as evidenced by, for example,U.S. Pat. No. 7,196,302 (“Laser Measuring Methods and Laser MeasuringSystem Having Fan-Shaped Tilted Laser Beams and Three Known Points ofPhotodetection System”) and U.S. Pat. No. 7,310,138 (“Method forAugmenting Radial Positioning System Using Single Fan Laser”), which areincorporated herein by reference. Multiple beam profiles may then beachieved for a single fan laser by adjusting and/or switching itsoptical components, or if multiple fan lasers are used, by selectivelyactivating a desired fan laser from an array of fan lasers, each laserhaving a different beam profile.

The laser pulses with the different beam profiles may be received at thetarget by a receiver 1600, an example of which is illustrated in FIG.16. The receiver 1600 is similar to commercially available laserreceivers, except it is configured to determine whether a requirednumber of laser beam profiles have been detected based on the differentencoding carried by each beam profile. As can be seen, the receiver 1600comprises, among other functional components, a timing system 1602, alaser detector 1604, a laser decoder 1606, and a receiver control system1608. One or more data buses 1610 may be provided to connect the variousfunctional components 1602-1608 together as needed. The laser detector1604 functions to detect laser pulses received by the receiver 1600, thelaser decoder 1606 functions to decode the laser pulses, and thereceiver control system 1608 functions to control operation of the laserdetector 1604 and the laser decoder 1606. An oscillator 1612 and a clocksignal generator 1614 may be provided in the timing system 1602 to allowthe timing system 1602 to regulate the internal operation of thereceiver 1600.

In accordance with aspects of the invention, a marksmanship module 1616may be provided in the receiver control system 1608 for some aspects ofthe invention. As with previous modules, this backrange module 1616 maybe a software module downloaded to and executed on the receiver controlsystem 1608, a hardware module fitted to or integrated with the receivercontrol system 1608, or a combination of both software and hardware. Themarksmanship module 1616 may also be one of several smaller componentsmaking up a larger overall software program and/or hardware component onthe receiver control system 1608. Such a marksmanship module 1616 maythen be operated to determine the marksmanship for laser pulses receivedat the receiver 1600.

General guidelines for operation of the marksmanship module 1616 areillustrated in the form of a flowchart 1700 in FIG. 17. As can be seen,the flowchart 1700 begins at block 1702 where the laser detector 1604 ismonitored for receipt of a laser pulse. At block 1704, a determinationis made as to whether a laser pulse has been detected. If the answer toblock 1704 is yes, then the received laser pulse is decoded at block1706 using decoding or demodulating techniques well known to thosehaving ordinary skill in the art. If the answer to block 1704 is no,then the flowchart 1700 returns to block 1702 where monitoring of thelaser detector 1604 may be continued.

Once the laser pulse has been decoded, a determination is made at block1708 as to whether a predefined number of laser beam profiles have beenreceived. For example, in an arrangement where there are four possiblelaser beam profiles, reception of all four beam profiles may be required(as evidenced by the encoding of the respective laser pulses) in orderfor a hit to be declared by the receiver 1600. Alternatively, three ofthe four beams, or perhaps only two of the four beams, may be sufficientin some cases for a hit to be declared by the receiver 1600, dependingon the particular application.

Whatever the beam profile requirement, if the answer to block 1708 isyes, then the engagement is processed as a hit at block 1710. Such a hitmay then be combined with range (or backrange) estimates to determinethe level of damage or lethality suffered by the target as needed. Onthe other hand, if the answer to block 1708 is no, then a determinationis made at block 1712 as to whether the engagement has expired based onone or more predefined criteria (e.g., elapsed time). If the engagementhas not expired, then the flowchart 1700 returns to block 1702 foradditional monitoring of the laser detector 1604. But if the engagementhas expired, then the beam profile count is cleared at block 1714, andthe process is restarted.

FIGS. 18A-18B illustrate an exemplary timing diagram and laser beamprofiles for a marksmanship determination aspects of the invention.Referring first to FIG. 18A, the horizontal lines 1800 and 1802 are timelines for two different beam profiles in a rangefinder that is capableof emitting laser beams having multiple profiles. The vertical lines,one of which is indicated at 1804, represent internal clock signals forthe rangefinder. The beam profiles in this example include ahorizontally oriented beam profile and a vertically oriented beamprofile. As can be seen, when the rangefinder is activated, it firesboth a laser pulse 1806 having the horizontally oriented beam profile aswell as a laser pulse 1808 having a vertically oriented beam profile.Each of these laser pulses 1806 and 1808 may have a different encodingor modulation scheme that allows a receiver to distinguish one laserpulse from the other laser pulse.

The beam profiles of the different laser pulses 1806 and 1808 areillustrated in FIG. 18B, where several targets 1810, 1812, and 1814 areshown in close proximity to one another in a clustered environment. Eachone of the targets 1810, 1812, and 1814 is equipped with a receiver1816, 1818, and 1820, respectively, of the type shown in FIG. 17 that iscapable of making marksmanship determination based on multiple laserbeam profiles. In this case, the intended target is the second target1812. Owing to the vertical and horizontally oriented beam profiles ofthe laser pulses 1806 and 1808 and the different spatial areas or zonescovered thereby, respectively, only the receiver 1818 for the secondtarget 1812 receives both laser pulses 1806 and 1808. This is indicatedin FIG. 18B by the overlapped or crosshatched area. As a result, it ispossible to unambiguously pair the second target 1812 with the shooterof the laser pulses 1806 and 1808 despite the close proximity of theadditional targets 1810 and 1814.

FIGS. 19A-19B are similar to FIGS. 18A-18B, respectively, except thatthere are now four different laser beam profiles. Referring first toFIG. 19A, the horizontal lines 1900, 1902, 1904, in 1906 are time linesfor a left fan laser, right fan laser, bottom fan laser, and top fanlaser, respectively. The vertical lines, one of which is indicated at1908, represent internal rangefinder clock signals. The beam profiles inthis example include a left shifted beam profile, a right shifted beamprofile, a bottom shifted beam profile, and a top shifted beam profile.As can be seen, when the rangefinder is activated, it fires a laserpulse 1910 having a left shifted beam profile, a laser pulse 1912 havinga right shifted beam profile, a laser beam 1914 having a bottom shiftedbeam profile, and a laser pulse 1916 having a top shifted beam profile.Note that the sequence with which the laser pulses 1910-1916 are firedis not important and need not be the same as the sequence describedhere. Each of the laser pulses 1910-1916 may have a different encodingor modulation scheme to allow a receiver to distinguish these laserpulses 1910-1916.

The beam profiles of the different laser pulses 1910-1916 areillustrated in FIG. 19B, where several targets 1918, 1920, and 1922 areshown in close proximity to one another in a clustered environment. Eachone of the targets 1918, 1920, and 1922 is equipped with a receiver (notseparately labeled for clarity purposes) of the type shown in FIG. 17that can make marksmanship determination based on multiple laser beamprofiles. As in the previous example, the intended target is the secondtarget 1920. By virtue of the different beam profiles and the differentspatial areas or zones covered thereby, respectively, only the secondtarget 1920 receives all four laser pulses 1910-1916, as indicated bythe overlapped or crosshatched area. This allows the second target 1920to be unambiguously paired with the shooter despite the close proximityof the remaining targets 1918 and 1922.

In some implementations, instead of separate or possibly co-locatedrangefinder 1500 and receiver 1600 as shown in FIGS. 15 and 16, therangefinder 1500 and the receiver 1600 may be combined into a singleintegrated marksmanship and rangefinder unit 2000, illustrated in FIG.20. As can be seen, this integrated marksmanship and rangefinder unit2000 comprises a timing system 2002, a laser detector 2004, a laserdecoder 2006, a control system 2008, and a fan laser transmitter 2010.One or more data buses 2012 may be provided to connect the variouscomponents 2002-2010 together as needed. The timing system 2002 providesthe clock signals that regulate the operation of the integratedmarksmanship and rangefinder unit 2000 and, for that purpose, mayinclude an oscillator 2014 and a clock signal generator 2016. Inaccordance with aspects of the invention, the control system 2008 mayinclude a marksmanship module 2018 for determining the marksmanship oflaser pulses received by integrated marksmanship and rangefinder unit2000. These components 2002-2018 of the integrated marksmanship andrangefinder unit 2000 operate in a similar manner to their counterpartsin FIGS. 15 and 16 and therefore a detailed description is not providedhere.

While the disclosed aspects of the invention have been described withreference to one or more specific implementations, those skilled in theart will recognize that many changes may be made. For example, althoughaspects of the invention have been described separately from oneanother, one or more of these aspects be combined with one or more otheraspects of the invention in a single implementation. In particular,aspects of the invention that are directed to cooperative backrangemeasurements may be combined with aspects of the invention that aredirected to marksmanship determination so as to form a single unit thatis capable of both determinations. This may be accomplished, forexample, by endowing the laser pulses shown in FIGS. 7A-7B and 13A-13Bwith different the beam profiles as described with respect to FIGS.18A-18B and 19A-19B.

Accordingly, each of the foregoing embodiments and obvious variationsthereof is contemplated as falling within the spirit and scope of thedifferent aspects of the invention, which are set forth in the followingclaims.

What is claimed is:
 1. A system for making laser-based cooperative timeof flight backrange measurements, comprising: first laser backrangefinder having a first clock signal and operable to emit a laser pulseupon occurrence of a predefined trigger event for a given engagement;and a receiver located an unspecified range from the first laserbackrange finder, the receiver having a second clock signal and operableto detect the laser pulse from the first laser rangefinder, the receiverhaving a range counter therein and configured to start the range counterupon occurrence of a predefined start counter event and to stop therange counter upon occurrence of a predefined stop counter event;wherein the first clock signal in the first laser backrange finder andthe second clock signal in the receiver are synchronized relative toeach other such that a preselected portion of a clock signal waveform ofthe first clock signal occurs at the same moment as either thepredefined start counter event at the receiver or the predefined stopcounter event at the second laser rangefinder; and wherein a countreached by the range counter of the receiver upon occurrence of thepredefined stop counter event determines a backrange from the receiverto the first laser rangefinder first laser backrange finder for thegiven engagement.
 2. The system according to claim 1, further comprisinga GPS-disciplined oscillator configured to provide a clock signal thathas been synchronized to a GPS clock signal.
 3. The system according toclaim 2, wherein the GPS-disciplined oscillator is in the first laserrangefinder first laser backrange finder and provides the first clocksignal, and the predefined trigger event includes reception of thepreselected portion of the clock signal waveform from theGPS-disciplined oscillator.
 4. The system according to claim 2, whereinthe GPS-disciplined oscillator is in the receiver and provides thesecond clock signal, the predefined start counter event includesreception of a preselected portion of a clock signal waveform from theGPS-disciplined oscillator, and the predefined stop counter eventincludes reception of the laser pulse from the first laser rangefinder.5. The system according to claim 2, wherein the GPS-disciplinedoscillator is in the receiver and provides the second clock signal, thepredefined start counter event includes reception of the laser pulsefrom the first laser rangefinder, and the predefined stop counter eventincludes reception of a preselected portion of a clock signal waveformfrom the GPS-disciplined oscillator.
 6. The system according to claim 2,wherein the GPS-disciplined oscillator is disciplined by a clock signalfrom one of the following: a GPS satellite, and GPS base station.
 7. Thesystem according to claim 1, wherein the laser pulse is a first laserpulse and the first laser backrange finder is configured to emit asecond laser pulse if a reflection of the first laser pulse is receivedat the first laser rangefinder.
 8. The system according to claim 7,wherein the first laser backrange finder is configured to emit thesecond laser pulse according to one of the following: immediately uponreceipt of the reflection of the first laser pulse, and after apredefined delay time.
 9. The system according to claim 8, wherein thepredefined start counter event includes reception of the first laserpulse at the receiver and the predefined stop counter event includesreception of the second laser pulse at the receiver second laserrangefinder.
 10. A method of making laser-based cooperative time offlight backrange measurements, comprising: synchronizing a first clocksignal in a first laser backrange finder in relation to a second clocksignal in a second laser rangefinder, the receiver being located anunspecified range from the first laser rangefinder; emitting a laserpulse from the first laser backrange finder upon occurrence of apredefined trigger event for a given engagement; detecting the emittedlaser pulse at the second laser rangefinder; starting a range counter atthe receiver upon occurrence of a predefined start counter event;stopping the range counter at the receiver upon occurrence of apredefined stop counter event; and using a count reached by the rangecounter upon occurrence of the predefined stop counter event todetermine a backrange from the receiver to the first laser backrangefinder for the given engagement; wherein a preselected portion of aclock signal waveform of the first clock signal occurs at the samemoment as either the predefined start counter event at the receiver orthe predefined stop counter event at the second laser rangefinder. 11.The method according to claim 10, further comprising generating a clocksignal from a GPS-disciplined oscillator, the clock signal having beensynchronized to a GPS clock signal.
 12. The method according to claim11, wherein the GPS-disciplined oscillator is in the first laserbackrange finder and provides the first clock signal, and the predefinedtrigger event includes reception of the preselected portion of the clocksignal waveform from the GPS-disciplined oscillator.
 13. The methodaccording to claim 11, wherein the GPS-disciplined clock is connected tothe receiver and provides the receiver clock signal, the predefinedstart counter event includes reception of a preselected portion of aclock signal waveform from the GPS-disciplined oscillator, and thepredefined stop counter event includes reception of the laser pulse fromthe first laser rangefinder.
 14. The method according to claim 11,wherein the GPS-disciplined oscillator is in the receiver and providesthe second clock signal, the predefined start counter event includesreception of the laser pulse from the first laser rangefinder, and thepredefined stop counter event includes reception of a preselectedportion of a clock signal waveform from the GPS-disciplined oscillator.15. The method according to claim 11, wherein the GPS-disciplinedoscillator is disciplined by a clock signal from one of the following: aGPS satellite, and GPS base station.
 16. The method according to claim10, wherein the laser pulse is a first laser pulse and the first laserbackrange finder is configured to emit a second laser pulse if areflection of the first laser pulse is received at the at the firstlaser rangefinder.
 17. The method according to claim 16, wherein thefirst laser backrange finder is configured to emit the second laserpulse according to one of the following: immediately upon receipt of thereflection of the first laser pulse, and after a predefined delay time.18. The method according to claim 17, wherein the predefined startcounter event includes reception of the first laser pulse at thereceiver and the predefined stop counter event includes reception of thesecond laser pulse at the second laser rangefinder.